Re: [patch] Important comment update to gcc/configure.in

[Alexandre Oliva <aoliva at redhat dot com>]

On Mar 14, 2003, Nathanael Nerode <neroden at twcny dot rr dot com> wrote:

> Ah, but that's what the version checks are for. :-)  For when we are
> building a brand new HOST->TARGET gas and can't run it.

Whenever HOST != BUILD, we need a BUILD->TARGET that the compiler is
going to use to build object files for the target.  Whether it's
exactly the same as the HOST->TARGET assembler we're about to build
doesn't matter all that much, but the assumption is that it's as close
an approximation as possible.  Since we're going to use this
BUILD->TARGET assembler at build time, and the resulting compiler is
going to use a HOST->TARGET assembler we're about to build, they'd
better be fully compatible, so it doesn't matter all that much how we
test the assembler.  We can test the BUILD->TARGET one for features,
or the HOST->TARGET one for version numbers, or both and pick the
worst (or flag in case they differ).  However, given the assumption
that they should be the same, I believe it's good enough to keep it
simple and just test the assembler for features.  In the Canadian
cross case, this means testing the BUILD->TARGET assembler.

> I certainly want to separate tests of the build->target assembler,
> used for building libgcc2, from tests of the host->target assembler,
> used to determine the behavior of the newly built gcc.  Those two
> things shouldn't be confounded

I suspect it would be nearly impossible to do away with the confusion,
and I actually fail to see the point of introducing so much
complication.  The proper procedure to build a Canadian cross is to
build BUILD->HOST, use that to build BUILD->TARGET, and then, using
both, build HOST->TARGET, so it's ok to assume BUILD->TARGET has the
same features as HOST->TARGET.

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                 aoliva at {redhat dot com, gcc.gnu.org}
CS PhD student at IC-Unicamp        oliva at {lsd dot ic dot unicamp dot br, gnu.org}
Free Software Evangelist                Professional serial bug killer